// 被观察者
class Subject {
    constructor() {
        this.state = 0;
        this.observers = [];
    }
    getState() {
        return this.state;
    }
    setState(state) {
        this.state = state;
        this.notifyAllObservers();
    }
    notifyAllObservers() {
        this.observers.forEach(observer => {
            observer.update()
        })
    }
    attach(observer) {
        this.observers.push(observer)
    }
}

// 观察者
class Observer {
    constructor(name, subject) {
        this.name = name;
        this.subject = subject;
        this.subject.attach(this);
    }
    update() {
        console.log(`${this.name} update, state ${this.subject.getState()}`)
    }
}

// 测试代码
let s = new Subject();
let o1 = new Observer('o1', s);
let o2 = new Observer('o2', s);
let o3 = new Observer('o3', s);

s.setState(1);